Differential Cqi Encoding for Cooperative Multipoint Feedback

1. A method, comprising: receiving in a mobile communication terminal signals from multiple cells that coordinate transmission of the signals with one another in a Cooperative Multipoint (CoMP) scheme; calculating in the terminal, based on the received signals, at least first and second Channel Quality Indicators (CQIs) for respective communication channels over which the signals are received, wherein the first or the second CQI is calculated for a communication channel from one of the cells that is designated for fallback to single-transmission-point transmission to the terminal; differentially encoding the second CQI relative to the first CQI; and transmitting feedback information, comprising the first CQI and the differentially-encoded second CQI, from the terminal.

2. The method according to claim 1 , wherein calculating the CQIs comprises identifying a strongest cell, whose signals are received in the terminal with a strongest signal strength among the multiple cells, and calculating the first CQI for a communication channel from the strongest cell to the terminal.

3. The method according to claim 1 , wherein calculating the CQIs comprises calculating the first and second CQIs for respective first and second communication channels from first and second ones of the cells to the terminal.

4. The method according to claim 1 , wherein calculating the CQIs comprises calculating one of the first and second CQIs for a communication channel from one of the cells to the terminal, and calculating the other of the first and second CQIs for an aggregate communication channel from the multiple cells to the terminal.

5. The method according to claim 1 , wherein differentially encoding the second CQI comprises encoding a difference between the second CQI and the first CQI, such that the differentially-encoded second CQI comprises a smaller number of bits than the second CQI.

6. The method according to claim 1 , wherein differentially encoding the second CQI comprises representing the differentially-encoded second CQI using no more than three bits.

7. The method according to claim 1 , wherein differentially encoding the second CQI comprises representing the differentially-encoded second CQI using no more than two bits.

8. Apparatus, comprising: a receiver, which is configured to receive signals from multiple cells that coordinate transmission of the signals with one another in a Cooperative Multipoint (CoMP) scheme; processing circuitry, which is configured to calculate, based on the received signals, at least first and second Channel Quality Indicators (CQIs) for respective communication channels over which the signals are received, wherein the first or the second CQI is calculated for a communication channel from one of the cells that is designated for fallback to single-transmission-point transmission to the receiver, and to differentially encode the second CQI relative to the first CQI; and a transmitter, which is configured to transmit feedback information comprising the first CQI and the differentially-encoded second CQI.

9. The apparatus according to claim 8 , wherein the processing circuitry is configured to identify a strongest cell, whose signals are received in the receiver with a strongest signal strength among the multiple cells, and to calculate the first CQI for a communication channel from the strongest cell to the receiver.

10. The apparatus according to claim 8 , wherein the processing circuitry is configured to calculate the first and second CQIs for respective first and second communication channels from first and second ones of the cells to the receiver.

11. The apparatus according to claim 8 , wherein the processing circuitry is configured to calculate one of the first and second CQIs for a communication channel from one of the cells to the receiver, and to calculate the other of the first and second CQIs for an aggregate communication channel from the multiple cells to the receiver.

12. The apparatus according to claim 8 , wherein the processing circuitry is configured to differentially encode the second CQI by encoding a difference between the second CQI and the first CQI, such that the differentially-encoded second CQI comprises a smaller number of bits than the second CQI.

13. The apparatus according to claim 8 , wherein the processing circuitry is configured to represent the differentially-encoded second CQI using no more than three bits.

14. The apparatus according to claim 8 , wherein the processing circuitry is configured to represent the differentially-encoded second CQI using no more than two bits.

15. A mobile communication terminal comprising the apparatus of claim 8 .

16. A chipset for processing signals in a mobile communication terminal, comprising the apparatus of claim 8 .